1. Field of the Invention
This invention relates to a rotary knock type mechanical pencil in which a lead feeding mechanism arranged in an outer cylindrical body including a forward outer cylinder and a rearward outer cylinder is operated to feed out a lead under a knock action by a relative rotation of these outer cylinders, and more particularly, a rotary knock type mechanical pencil in which the lead feeding mechanism within the body can perform a smooth and positive lead feeding operation under a relative rotation of the forward and rearward outer cylinders.
2. Description of the Prior Art
In recent years, various types of knock type mechanical pencils provided with some superior mechanisms such as an automatic lead feeding mechanism, an extremity end knock mechanism or the like have been proposed in the mechanical pencil field. These knock type mechanical pencils have, on the one hand, proved dependable for consumers due to ease and positiveness in operation and on the other hand, have some disadvantages in that the design spoils the outer aesthetic appearance due to the need to arrange a knock operating part either at an upper end of the body or at an outer circumferential side of the body. In view of this fact, there has been proposed a rotary slide type of rotary knock type mechanical pencil having both a better outer appearance and a function superiority.
The conventional type of the above-mentioned rotary knock type mechanical pencil is composed of a forward outer cylinder provided with a lead feeding mechanism at its inner extremity end side and a rearward outer cylinder having a cam cylinder therein which are rotatably connected to each other. This rotary knock type mechanical pencil is operated such that a writer holds one outer cylinder and the other outer cylinder is rotated in any direction, thereby the cam cylinder is rotated in a circumferential direction by a specified range, and the cam surface of the cam cylinder reciprocates an extended rod of the lead feeding mechanism abutting against the cam surface, resulting in generating a so-called cam movement. An operating force in a reciprocating direction converted from the cam movement may perform the knock operation of the lead feeding mechanism, resulting in that the lead is fed out of an extremity end of the mechanical pencil under the knock action.
Examples of the conventional type of rotary knock type mechanical pencil described above, are disclosed U.S. Pat. No. 4,269,524 and U.S. Pat. No. 4,362,410. These patents disclose that each of the forward and rearward outer cylinders is connected to each other in such a way as they may be rotated relative to each other. As shown in U.S. Pat. No. 4,269,524, a lead feeding mechanism is provided for feeding lead responsive to the operation of a rotary cylinder 124, within the outer cylinder, which acts on a cam cylinder having a slant surface 132 which is abutted against an extending rod 13 of the feeding mechanism which is formed with a cam surface at its extremity end side to convert the rotary movement into a reciprocating movement.
However, according to the rotary knock type mechanical pencil described in the above-mentioned U.S. Pat. No. 4,269,524, a lead feeding mechanism such as a tightening member receiver 113 a tightening member 11 and a chuck 19 or the like is integrally formed with a lead case 20 at the rear end of the chuck, and in case of performing a lead feeding operation, so-called knock operation, all the component elements positioned at the inner central side of the mechanical pencil perform a reciprocating movement. Since the lead case 20 is set at its position by only a spring S.sub.1 within the rotary cylinder 124, a looseness is generated at the lead feeding mechanism within the mechanical pencil during the reciprocating movement and so a positive lead feeding operation can not be performed.
Secondly, the rotary cylinder 124 directly advances or retracts the tightening member receiver 113 through the extend rod 13 via its slant surface 132. Since this tightening receiver 113 advances or retracts to cause the tightening member 11 to fasten the chuck 19 or to release the fastening operation, a lead feeding operation of the tightening member 11 while being released from the chuck 19 is merely performed by chance, and a lead feeding operation with the rotary knock type mechanical pencil having this mechanism can be performed only in the case that the lead L drops together with the lead retainer 18 downwardly via extremity end of the mechanical pencil and so it has a problem that a positive lead feeding operation can not be performed.
Thirdly, although the mechanical pencil of U.S. Pat. No. 4,269,524 has an advantage of requiring a fewer number of component elements, it has another problem that irrespective of the constitution having less number of parts, for example, it is necessary to form a guide groove 10, a projection 12, a receiving member 120 and a projection 121 or the like so as to guide a reciprocating movement of the lead feeding mechanism, resulting in a complex structure.
Fourthly, according to the patent, since a lead L is set for its position while the rotary cylinder 124 is rotated and the chuck 19 is fastened with the tightening member receiver 113 and the tightening member 11 so as to perform a writing operation, it shows a problem that in case of a quite strong writing pressure of the writer, this strong writing pressure can not be dampened, the lead is frequently broken and under the worst condition the lead feeding mechanism or rotary mechanism is detrimentally affected.